Genome-wide survey and expression analysis of the stress-associated protein gene family in desert poplar, <Emphasis Type="Italic">Populus euphratica</Emphasis>

Stress-associated proteins (SAPs) are a novel class of zinc finger proteins that extensively participate in abiotic stress responses. To date, no overall analysis and expression profiling of SAP genes in woody plants have been reported. Populus euphratica is distributed in desert regions and is extraordinarily adaptable to abiotic stresses. Thus, it is regarded as a promising candidate for studying abiotic stress resistance mechanisms of woody plants. In this study, 18 non-redundant SAP genes were identified from the genome of P. euphratica using basic local alignment search tool algorithms and functional domain verification. Among these 18 PeuSAP genes, 15 were intronless. To investigate the evolutionary relationships of SAP genes in P. euphratica and other Salicaceae plants, phylogenetic analyses were performed. Subsequently, the expression profiles of the 18 PeuSAP genes were analyzed in different tissues and under various stresses (drought, salt, heat, cold, and abscisic acid (ABA) treatment) using quantitative real-time PCR. Tissue expression analysis indicated that PeuSAPs showed no tissue specificity. PeuSAPs were induced by multiple abiotic stresses, especially drought, salt, and heat stresses, perhaps because of abundant cis-acting heat shock elements and drought-inducible elements in the promoter regions of the PeuSAPs. Moreover, single nucleotide polymorphisms (SNPs) variant analysis revealed many synonymous and non-synonymous SNPs in PeuSAP genes, but the zinc finger structure was conserved during evolution. These results provide an overview of the SAP gene family in P. euphratica and a reference for further functional research on PeuSAP genes.     

Effect of shade on leaf photosynthetic capacity,light-intercepting,electron transfer and energy distribution of soybeans

Lectin receptor-like kinases (LecRLK) are widespread in higher plants and their effects on abiotic stress tolerance are gradually being reported. However, little information is available on LecRLK functions in bryophytes. Here, an L-type LecRLK gene (PnLecRLK1) was characterized from the Antarctic moss Pohlia nutans. Subcellular localization analysis revealed that PnLecRLK1 was a plasma membrane protein. The expression of PnLecRLK1 was rapidly induced by simulated cold, salt, and drought stresses as well as by exogenously applied abscisic acid (ABA) and methyl jasmonate. Transgenic Arabidopsis plants of overexpressing PnLecRLK1 exhibited enhanced tolerance to chilling-stress and increased ABA sensitivity. Additionally, the expression levels of genes in the C-repeat binding factor (CBF) signaling pathway such as AtCBF1, AtCBF2, AtCBF3 and AtCOR47 were markedly increased in transgenic Arabidopsis. Furthermore, the expression levels of ABA-responsive genes, such as AtABI4, AtABI5, AtMYB2 and AtDREB2A, were also significantly up-regulated in transgenic Arabidopsis. Therefore, our results suggested that PnLecRLK1 functions as a membrane-bound regulator that increases chilling stress tolerance and ABA sensitivity to enable P. nutans to adapt to polar climates.     

Overexpression of <Emphasis Type="Italic">OsDT11</Emphasis>, which encodes a novel cysteine-rich peptide,enhances drought tolerance and increases ABA concentration in rice

Short-chain peptides play important roles in plant development and responses to abiotic and biotic stresses. Here, we characterized a gene of unknown function termed OsDT11, which encodes an 88 amino acid short-chain peptide and belongs to the cysteine-rich peptide family. It was found that the expression of OsDT11 can be activated by polyethylene glycol (PEG) treatment. Compared with wild-type lines, the OsDT11-overexpression lines displayed dramatically enhanced tolerance to drought and had reduced water loss, reduced stomatal density, and an increased the concentration of abscisic acid (ABA). The suppression of OsDT11 expression resulted in an increased sensitivity to drought compared to wild-type expression. Several drought-related genes, including genes encoding abscisic acid (ABA) signaling markers, were also strongly induced in the OsDT11-overexpressing lines. Moreover, the expression of OsDT11 was repressed in ABA-insensitive mutant Osbzip23 and Os2H16 RNAi lines. These results suggest that OsDT11-mediated drought tolerance may be dependent on the ABA signaling pathway.     

Characterization and comparative expression analysis of <Emphasis Type="Italic">CUL1</Emphasis> genes in rice

Cullin-RING E3 ubiquitin ligase (CRL) complex is known as the largest family of E3 ligases. The most widely characterized CRL, SCF complex (CRL1), utilizes CUL1 as a scaffold protein to assemble the complex components. To better understand CRL1-mediated cellular processes in rice, three CUL1 genes (OsCUL1s) were isolated in Oryza sativa. Although all OsCUL1 proteins exhibited high levels of amino acid similarities with each other, OsCUL1-3 had a somewhat distinct structure from OsCUL1-1 and OsCUL1-2. Basal expression levels of OsCUL1-3 were much lower than those of OsCUL1-1 and OsCUL1-2 in all selected samples, showing that OsCUL1-1 and OsCUL1-2 play predominant roles relative to OsCUL1-3 in rice. OsCUL1-1 and OsCUL1-2 genes were commonly upregulated in dry seeds and by ABA and salt/drought stresses, implying their involvement in ABA-mediated processes. These genes also showed similar expression patterns in response to various hormones and abiotic stresses, alluding to their functional redundancy. Expression of the OsCUL1-3 gene was also induced in dry seeds and by ABA-related salt and drought stresses, implying their participation in ABA responses. However, its expression pattern in response to hormones and abiotic stresses was somehow different from those of the OsCUL1-1 and OsCUL1-2 genes. Taken together, these findings suggest that the biological role and function of OsCUL1-3 may be distinct from those of OsCUL1-1 and OsCUL1-2. The results of expression analysis of OsCUL1 genes in this study will serve as a useful platform to better understand overlapping and distinct roles of OsCUL1 proteins and CRL1-mediated cellular processes in rice plants.     

Transcriptome and physiological analyses reveal that AM1 as an ABA-mimicking ligand improves drought resistance in <Emphasis Type="Italic">Brassica napus</Emphasis>

Abscisic acid (ABA) is the most important stress hormone in the regulation of plant adaptation to drought. Owing to the chemical instability and rapid catabolism of ABA, ABA mimic 1 (AM1) is frequently applied to enhance drought resistance in plants, but the molecular mechanisms governed by AM1 on improving drought resistance in Brassica napus are not entirely understood. To investigate the effect of AM1 on drought resistance at the physiological and molecular levels, exogenous ABA and AM1 were applied to the leaves of two B. napus genotypes (Q2 and Qinyou 8) given progressive drought stress. The results showed that the leaves of 50 µM ABA- and AM1-treated plants shared over 60% differential expressed genes and 90% of the enriched functional pathways in Qinyou 8 under drought. AM1 affected the expression of the genes involved in ABA signaling; they down-regulated pyrabactin resistance/PYR1-like (PYR/PYLs), up-regulated type 2C protein phosphatases (PP2Cs), partially up-regulated sucrose non-fermenting 1-related protein kinase 2s (SnRK2s), and down-regulated ABA-responsive element (ABRE)-binding protein/ABRE-binding factors (AREB/ABFs). Additionally, AM1 treatment repressed the expression of photosynthesis-related genes, those mainly associated with the light reaction process. Moreover, AM1 decreased the stomatal conductance, the net photosynthetic rate, and the transpiration rate, but increased the relative water content in leaves and increased survival rates of two genotypes under drought stress. Our findings suggest that AM1 has a potential to improve drought resistance in B. napus by triggering molecular and physiological responses to reduce water loss and impair growth, leading to increased survival rates.     

Identification and comparative analysis of <Emphasis Type="Italic">Brassica juncea</Emphasis> pathogenesis-related genes in response to hormonal,biotic and abiotic stresses

Pathogenesis-related proteins (PRs) are the antimicrobial proteins which are commonly used as signatures of defense signaling pathways and systemic acquired resistance. However, in Brassica juncea most of the PR proteins have not been fully characterized and remains largely enigmatic. In this study, full-length cDNA sequences of SA (PR1, PR2, PR5) and JA (PR3, PR12 and PR13) marker genes were isolated from B. juncea and were named as BjPR proteins. BjPR proteins showed maximum identity with known PR proteins of Brassica species. Further, expression profiling of BjPR genes were investigated after hormonal, biotic and abiotic stresses. Pre-treatment with SA and JA stimulators downregulates each other signature genes suggesting an antagonistic relationship between SA and JA in B. juncea. After abscisic acid (ABA) treatment, SA signatures were downregulated while as JA signature genes were upregulated. During Erysiphe cruciferarum infection, SA- and JA-dependent BjPR genes showed distinct expression pattern both locally and systemically, thus suggesting the activation of SA- and JA-dependent signaling pathways. Further, expression of SA marker genes decreases while as JA-responsive genes increases during drought stress. Interestingly, both SA and JA signature genes were induced after salt stress. We also found that BjPR genes displayed ABA-independent gene expression pattern during abiotic stresses thus providing the evidence of SA/JA cross talk. Further, in silico analysis of the upstream regions (1.5 kb) of both SA and JA marker genes showed important cis-regulatory elements related to biotic, abiotic and hormonal stresses.